improve output in error case

pre_commit/util.py

@@ -108,15 +108,23 @@ class CalledProcessError(RuntimeError):
         self.output = output
 
     def __str__(self):
+        output = []
+        for text in self.output:
+            if text:
+                output.append('\n    ' + text.replace('\n', '\n    '))
+            else:
+                output.append('(none)')
+
         return (
             'Command: {0!r}\n'
             'Return code: {1}\n'
             'Expected return code: {2}\n'
-            'Output: {3!r}\n'.format(
+            'Output: {3}\n'
+            'Errors: {4}\n'.format(
                 self.cmd,
                 self.returncode,
                 self.expected_returncode,
-                self.output,
+                *output
             )
         )
 

tests/prefixed_command_runner_test.py

@@ -19,7 +19,23 @@ def test_CalledProcessError_str():
         "Command: ['git', 'status']\n"
         "Return code: 1\n"
         "Expected return code: 0\n"
-        "Output: ('stdout', 'stderr')\n"
+        "Output: \n"
+        "    stdout\n"
+        "Errors: \n"
+        "    stderr\n"
+    )
+
+
+def test_CalledProcessError_str_nooutput():
+    error = CalledProcessError(
+        1, [str('git'), str('status')], 0, (str(''), str(''))
+    )
+    assert str(error) == (
+        "Command: ['git', 'status']\n"
+        "Return code: 1\n"
+        "Expected return code: 0\n"
+        "Output: (none)\n"
+        "Errors: (none)\n"
     )